SKB EP MIKO-21 SKB MIKO-21 MicroOhm Tester (200A)

• in high-voltage circuit breaker contacts,
• in disconnecting switches, separators, and short-circuiters,
• in packaged switchgears,
• in contact couplings,
• in weld seams, etc.

One of the problems faced when measuring the transient resistances with permissible error is availability of oxide films between contact surfaces.

According to International standard IEC 60694 "General Specifications for High-Voltage Switch Gears" (International Electrotechnical Commission), for controlling this type of error, amperage of the test current during testing the electric resistance in the main circuit of a HV circuit breaker shall be between 50A and its rated value.

Current amperage in the passport data of many foreign circuit breakers is most often limited by specific values: 100A and 200A.

Amperage in the MIKO-21 can be set in several ways:

• By selecting from a number of specified values: 10A, 50A, 100A, and 200A;
• By setting the automatic mode for selecting the  test amperage;
• Manual mode for setting the test current in the range from 1 to 200 A at a step of 1A.

Only SKB EP microohmmeters measure transient resistances (R _transient) of minimum-oil and bulk-oil circuit breakers using separate automatic modes optimized for those circuit breakers.  Current transformers (CT) of bulk-oil circuit breakers form a prolonged transition process when the test current is applied. For this reason the time of measurement is determined by CT parameters, by their number, amperage and, for example, for  U-220-2000-25U1 circuit breaker it may be as high as 30 seconds. Special algorithms with automatic stop of measurements allow avoidance of subjective mistakes and increase the number of measurements per one battery charge.

There are four methods programmed in the instrument for resistance measurement start-up:

• "Single-shot start-up", i.e., start-up by pressing START button located on the front panel of the instrument.  For implementing this method the test cable clamps are first firmly fastened on the tested object and only then the user starts up measurements.
• "Start-up against circuit closing". In this case the measurement is started up after occurrence of electric contact between tested circuit and current or potential contacts of the test cable. Information obtained is displayed.  This mode is used together with needle-type press contact of the test cable and is intended for rapid testing of a large number of bolt joints.
• "Regular star-up". Measurements are started up in the pre-specified time intervals.  This mode can be used for items rejecting.  The mode is used in the following cases:  when both hands are used for pressing the cable probe against the test points and there is nobody else to press the START button; for monitoring the changing resistance, e.g., during tuning; for rejecting the kit of resistors against limiting values of resistance specified in the instrument.
• "Regular circuit". This mode is intended for regular automatic measurement start-up against the test circuit closing.  The mode is initiated by pressing the START button; the measurement is started against the test circuit closing, and the instrument gives a beep.  After getting the result the software automatically converts to the mode of waiting for the next circuit closing.

Company archive of passport values of resistances (R _transient) of circuit breaker contacts ensures automatic comparison between measured and passport values subject to circuit breaker grade indication;

Archive of the instrument contains passports of HV circuit breakers with indication of maximum and/or minimum permissible transient resistances of contacts, and passports for rejected resistors with indication of permissible values of the upper and lower thresholds of resistances.

The user can also add the required template.

Availability of an in-built archive of passport values of eclectic resistances (main circuit of HV circuit breakers) facilitates automatic detection, and the device beeps if the results of measurements go beyond the permissible limits.

Color graphic display of high brightness ensures easy reading on a sunny day, whereas intuitively understandable interface with a sensor display facilitates the instrument use.

The Instrument can be manipulated either from the film keyboard or from the sensor display, as suits.

Communication with PC via USB or a flash card facilitates data transfer from the Instrument to the Company data base.

The instrument can be built-in into testing systems under control of software complexes of diagnosis laboratories and equipment manufacturers.

• Availability of an energy-independent memory and a mode of "automatic storage of the results of measurements" considerably reduce the full time of the circuit breaker test owing to transfer of the data obtained from the substation area to the Company office.
• The above peculiarities ensure complete independence and high mobility of the instrument over the vast substation or workshop territory as you avoid troubles with a power cable, extension rod to the socket, and grounding.

For convenience the standard kit includes only one type of a test package (Kit 3 includes two test cables with crocodile clips for high-voltage circuit breakers up to 110 kV).

Suitable cable or a set of cables can be selected from a large range of additional accessories:

• Test cable, should the instrument be placed near a circuit breaker:

One set with spring-loaded contacts for measurements in busbars or in arc extinguish chambers.  Two other kits with crocodile clips (with current and potential wires) for circuit breakers of up to 10 kV, circuit breakers of up to 110 kV, and a part for circuit breakers of up to 220kV.

• Test cable, should the instrument be placed in the lifter cradle:

Three kits that include cables with crocodile clips (with current and potential wires), a cable with a G-clamp (with current and potential wires). They differ in length and purpose, namely: for HV circuit breakers of up to 220kV, for HV circuit breakers of up to 330kV, some for 500kV, and for HV circuit breakers of up to 750kV.

• Test cables for precision measurements and measurements on the circuit sections with the test current is applied to their end points.
•  

• Specifications	Value
  Range of resistance measurements, Ohm	0.1 µΩ ÷ 2 Ω
  Range of test current amperage, A	1 ÷ 200
  Error of measurements, %	±0.05
  Time of measurement in Mode 1, sec	not more than 2.0
  Time of measurement in Mode 2 on a bulk-oil circuit breaker, sec	10 ÷ 30
  Time of measurement in Mode 3 on a bulk-oil circuit breaker with battery charge saving	5 ÷ 15
  Period of continuous operation (in normal conditions), hrs, no less than	8
  Number of tests (in normal conditions), no less than	500
  Display of the instrument	Sensor, color, graphic, 480x272 dots
  Types of data transfer channels	USB/USB Flash
  Consumed power does not exceed, V	60
  Operating temperature range, ºС	-20 ÷ +50
  Weight of the test block, kg, not more than	3.1
  Dimensions, mm	270х250х130
  Interface language	English
  User manuals language	English
  Calibration period, year	3